It is known that sliding discharge gates for ladles and in general for large-sized containers of liquid metal, are used with ever increasing frequency in foundries.
In fact, compared to rod gates, which are still used in many old-fashioned plants, sliding discharge gates have the advantages of allowing the flow of steel which issues from the base of the ladle to be controlled more precisely, on the one hand, and on the other hand, permit the refractories of the discharge gate to be replaced while working from the outside of the ladle and thus without waiting for the ladle to be cooled down. As a result the sliding discharge gate have better operative characteristics and allow maintenance to be carried out more rapidly.
It is also known that sliding discharge gates in general have a first, fixed metallic support plate arranged below the base of the ladle, on whose lower face is fixed in any suitable manner a first stationary refractory brick whose centre is apertured and through which passes the jet of liquid steel when the discharge gate is in the open position. Said first fixed plate supports, in an adjustable manner by way of a suitable series of bolts, a second metallic support plate which is also fixed in the operative position of the discharge gate.
The second fixed plate also has a large aperture in the centre for the passage of the liquid metal; the function of said second fixed plate is to define, with the first metallic fixed plate, a horizontal space in which a third slidable metallic support plate slides.
On said third slidable plate is fixed a second apertured refractory brick which is slidable together with said slidable plate; when the apertures of the first and second bricks are aligned, the discharge gate is in the open position; when on the other hand the apertures of the two bricks are not aligned and not even partially in register, the sliding discharge gate is closed. It is apparent that in such a closed position, the seal of the discharge gate is entirely due to the seal effected between the opposed faces and the contact between the two refractory bricks.
Having regard to the pressure applied by the metallic liquid above, it is not only necessary that the two opposed surfaces of the two refractory bricks be coplanar and in contact, but these surfaces must be pressed one against the other by the most uniform contact pressure possible over the whole of said contact surface. It results that at the moment of assembling the sliding discharge gate, the bolts by means of which one determines the distance between the first and second plates and hence the pressure exercised by the second plate on the third, moveable plate which is in turn thrust against the lower face of the first fixed plate, or upper plate, must be tightened with great care by means of torque wrenches; this requires a relatively long time; the time necessary for regulating the tightening force of the bolts has an important effect on the cost of using the sliding discharge gate, given that said adjustment need not only be carried out when assembling the slide. The refractory bricks referred to above, supported respectively by the first, upper fixed plate and by the third, intermediate, slidable plate wear out after a certain period of operation and thus must be replaced; for each replacement; it is necessary to open the sliding discharge gate and repeat the operation to tightening the bolts which serve to press the slidable refractory brick against the fixed refractory brick.